MySQL instance lost when upgrading to Windows 10
You can manually put the service back as follows:
STEP 01) Open the Windows CLI as Administrator
STEP 02) cd C:\Program Files (x86)\MySQL\MySQL 5.6\bin
or wherever mysqld.exe
resides
STEP 03) Reinstall the service
mysqld --install
That's it.
I have mentioned this before in ServerFault and DBA StackExchange
GIVE IT A TRY !!!